# Pharmacokinetics of Ampicillin Trihydrate in Plasma, Interstitial, and Peritoneal Fluid Following Intraperitoneal or Intramuscular Administration in Steers at the Beginning of a Standing Flank Laparotomy

## TL;DR

This study compares how ampicillin trihydrate reaches infection sites in cattle after different administration methods, finding that intraperitoneal delivery results in higher drug concentrations in the abdominal area.

## Contribution

The study provides new pharmacokinetic data on ampicillin trihydrate in cattle following intraperitoneal versus intramuscular administration.

## Key findings

- Intraperitoneal administration resulted in significantly higher plasma concentrations of ampicillin compared to intramuscular delivery.
- Peritoneal fluid concentrations were higher with intraperitoneal administration, but there was high variability in pharmacokinetic parameters.
- The study highlights the need for further research on the clinical efficacy of intraperitoneal ampicillin in cattle.

## Abstract

Prophylactic and perioperative use of antibiotics is common prior to abdominal surgery in cattle for minimizing the risk of postoperative infections. Yet, there is little information on drug concentrations at sites of potential infections following surgical procedures. The objective of this study was to compare the concentrations in the plasma, peritoneal fluid, and interstitial fluid of ampicillin trihydrate in cattle. In a randomized design, ampicillin trihydrate, a β‐lactam antibiotic, was administered to 12 healthy Holstein‐Friesian steers intraoperatively via intraperitoneal (IP; n = 6) or intramuscular (IM; n = 6) injection in the cervical neck muscles at 11 mg/kg for both groups. For IP administration, ampicillin trihydrate was deposited into the abdominal cavity following an incision in the right paralumbar fossa. Steers in the IM group were administered ampicillin prior to surgical closure. Peritoneal fluid and interstitial fluid were collected using ultrafiltration probes. IP administration achieved higher concentrations in peritoneal fluid as compared to IM administration. Maximum plasma concentrations were significantly higher following IP administration (3.11 ± 2.5 μg/mL; p < 0.004) compared to the IM group (0.05 ± 10.9 μg/mL). Despite high peritoneal fluid concentrations of ampicillin, the variability in critical pharmacokinetic parameters following IP administration raises concerns about its therapeutic reliability. The correlation between intraperitoneal drug concentrations and clinical efficacy warrants further investigation.